This is something that started after I moved the game on to a 64-bit Windows 7 Home Premium Dell laptop. It's not that they don't appear whether they're switch on or not, but but that the entire dialog box for that command is greyed out so I can't change the settings, which are set to off.

True, because the gridlines only worked passably on the four original battlesets. If the code is ever expanded to work for the rest of the world (or to notice which battleset the player is using) then the dialog will be re-enabled.

IIRC, gridlines worked in all the battlesets in my old 32-bit machine. They certainly did in WestPac, where I used them as a reference for setting recurring patrols. It was only after reinstalling the game on a newer 64-bit machine that this problem popped up.